Biomécanique de l’os. Application au traitement des fractures

Abstract

Bone is a living anisotropic and viscoelastic material. Bone remodels in response to the mechanical demands placed upon it (Wolff’s law). Bone strength varies according to the direction in which the load is imposed. Bone is weaker in tension than in compression. Muscle activity alters the in vivo stress pattern in bone. Bone healing is influenced by mechanical factors. The most extensive question is the choice between stable or unstable fixation: the osteosynthesis is static if the stiffness never changes during the fracture healing. In an open fracture site a static osteosynthesis must be stable. The osteosynthesis is dynamic when its stiffness vary during the fracture repair in order to improve the callus formation or to reduce the risk of refracture (nail and external fixator). The dynamic osteosynthesis can be slightly unstable during 5 or 6 weeks in order to enhance the periosteal callus and after that stable until the end of the fracture healing. The amount of instability which improves the healing is still unknown. The experience suggests that it must be moderate.